The invention relates to the field of metallurgy and metal alloy mechanical hinges. More particularly, the present invention relates to shape memory alloys trained as hinges for compressed stowing and recoiled deploying of three-dimensional enclosure of panels.
The development of microsatellites and nanosatellites low earth orbits requires the collection of sufficient power for onboard instruments with low weight in a low volume spacecraft. Power generation methods for very small satellites of less that ten kilograms are desirable for these small satellites. Thin film solar arrays are useful power sources for small satellites. One problem faced by these low weight and low volume spacecraft is the collection of sufficient power for onboard instruments and propulsion. Body-mounted solar cells may be incapable of providing enough power when the overall surface area of a microsatellite or nanosatellite is small. Deployment of traditional planar rigid large solar arrays necessitates larger satellite volumes and weights and also requires extra apparatus needed for attitude pointing. One way to provide power to a small spacecraft is the use of roughly spherical deployable power system such as a solar powersphere that offers a relatively high collection area with low weight and low stowage volume without the need for a solar array pointing mechanism. The powersphere deployment scheme requires a deployment hinge that would move the individual hexagon and pentagon flat panels of the powersphere from a stacked configuration to an unfolded configuration where the individual panels would form a spherical structure resembling a soccer ball upon completion of the deployment sequence. The powersphere requires deployment hinges that serve to move the individual hexagon and pentagon flat panels of the powersphere from a stacked configuration to an unfolded configuration where the individual panels would form a spherical structure upon completion of the deployment sequence. Each of the panels has at least one hinge to adjacent panels. The panels should be locked into place and maintained at a precise angle relative to each connected panel to form the spherical shape. The flat hexagon and pentagon panels approximate an omnidirectional sphere. A combination of hexagon and pentagon shaped panels are used to form a soccer ball panel configuration when fully deployed. The interconnecting deployment hinges serve to position the individual flat panels of the powersphere from a stacked configuration to the deployed position forming the sphere of solar panels. The panels are hinged to one another and deploy to a precise angular position into the final shape that is preferably spherical rather than oblong or some other undesirable shape. Ideally this deployment mechanism would be fabricated from a thin film material that would have the properties to effect the mechanical positioning deployment and serve as structural elements for holding and locking each of the panels in respective positions about the powersphere.
Another type of microsatellite having an power enclosure uses a powerbox that is a three-dimensional solar array shape having rectangular shaped flat panels that would also deploy from a stowed flat configuration into a box shape configuration. The powerbox consists ideally of similarly shaped panels interconnected with hinges fabricated from a thin material that would have the properties to perfect the mechanical deployment and also be a structural element for locking each of the panels into respective positions. Hence, the powerbox would also require hinges that serve to move and lock the flat solar panels into position during deployment. Regardless of the final exterior shape of the three-dimensional power enclosure of a nanosatellite or microsatellite, a hinge mechanism is needed for deployment of the flat solar panels to cause the transition from the stowed configuration to the desired final array shape. Hence, there exists a need for positioning hinges between the flat panels forming a power collecting enclosure formed from the deployed solar array flat panels to realize any number of complex three dimensional solar array exterior surfaces used for solar power collection. However, the interconnecting hinges present a power conduction problem of routing collected converted power from the flat solar array panels to the payload of the spacecraft. Electrical conductivity of the hinge could be used to route signals and power about the power enclosure without the use of separate power lines for communicating power from the solar cell panels to the spacecraft payload. The hinges should be made of conventional materials. The hinge material could be a polymer as a flexure type hinge. But polymers are unstable and relax by cold flowing when stressed for any length of time. Polymer materials can also have undesirable outgassing properties and are generally not good electrical conductors. Polymer materials also have very low Young""s moduli that reduces the deployment energy that can be stored in the hinge while stowed and later used to deploy and position the panels. Spring metals such as hardened stainless steel, beryllium copper or phosphorous bronze are commonly used as flexure type spring hinges. These spring metals have large Young""s moduli, low outgassing characteristics, good electrical conductivity and will not cold flow, but spring metals have very small maximum elastic strains of 1% or less, and hence are unsuitable as deployment hinges because the steel spring hinges with interconnected panels will not stow compactly. These and other disadvantages are solved or reduced using the invention.
An object of the invention is to provide a deployment hinge for interconnecting and deploying panels from a stowed configuration into a deployment configuration.
Another object of the invention is to provide a deployment conductive hinge for mechanically and electrically interconnecting and deploying solar cell panels from a stowed configuration into a deployment configuration.
Yet another object of the invention is to provide an integral deployment latch for locking deployed panels into a deployment configuration.
Still another object of the invention is to provide a conductive deployment latching hinge for mechanically moving and locking and electrically interconnecting panels into a deployment configuration forming a power enclosure of a satellite.
Yet another object of the invention is to provide a compact hinge for interconnecting thin film solar panels, for enabling the panels to be stowed compactly, and for unfolding the panels into a large area three-dimensional array of a predetermined shape.
A further object of the invention is to store the energy necessary within an interconnecting hinge for unfolding and deploying the thin film solar array panels into a three-dimensional shape.
Still a further object of the invention is to use the hinges as the conductors for daisy chaining thin film solar cell panels together for conducting electrical power from the panels to a satellite power system.
Yet a further object of the invention is to provide an integral latch hinge for locking deployed panels in place for stiffening and strengthening a panel structure.
The invention is directed to a conductive hinge and latch for mechanically and electrically interconnecting and deploying panels into a deployed configuration. In a first aspect, the conductive hinge is made of a shape memory alloy with superelastic material properties enabling a small radius bend during stowage and flexible recoil return to a trained rigid hinge deployment position. In a second aspect of the invention, the hinge is further adapted into a latch for holding the hinge in a locked position after release and recoiling to rigidly locked panels into the deployment configuration. In a third aspect, the hinge is an electrical conductor enabling the hinge to function as a power bus for routing current through multiple interconnected panels to a power system the satellite payload. The hinge is sufficiently conductive enabling the use of the hinge as a solar array power bus.
The multiple panels may be thin film flexible solar cell panels forming a hinged solar cell array that is deployed when the hinges are released from the bent stowed position into the latched rigid deployed position. Thin film solar cell arrays use extremely thin film amorphous silicon active materials. Hence, the hinge is also made equally thin as a thin film material. In order to stow thin film solar cell arrays in the most compact manner, the hinge is made of an extremely flexible superelastic shape memory alloy. To minimize the stowing volume, the hinges should be made as small as possible and the hinge will allow the panels to lie flat on top of each other.
The shape memory metal deployment hinge is preferably used for the square and rectangular solar panels forming a powerbox solar cell array, but can be used for other interconnected solar cell panel arrays such as the powersphere comprising hexagon and pentagon flat solar cell panels. The flat panels that make up a thin film deployable solar array enclosure are preferably stowed in the stack during the launch phase of a space satellite. Once on orbit, the stack of flat panels is deployed using the stored energy in the hinges so that the panels take a predetermined shape such as a rectangular powerbox or spherical powersphere. The hinge is capable of supplying the mechanical energy required to cause the stowed stack of flat panels to move and unfurl, that is recoil, to the deployed position.
The shape memory deployment metal hinge is preferably a thin sheet nitinol (NiTi) alloy used as a deployment spring, a structural support and a locking latch. Thin sheets of the nitinol alloy can be used as a spring and can be bent around extremely small radius without breakage or permanent deformation. The shape memory alloy hinge is disposed between adjacent thin film solar cell panels and can be bent to a small radius enabling the panels to stack one on top of the other with minimal spacing and therefore with maximum stowage efficiency. When stowed, the panels preferably rest on each other with no space in between the panels in order to be less susceptible to launch vibration damage and for stowage volume efficiency. The shape memory metal alloy returns when released to a trained precise angle required for the connection of the panels into the predetermined three-dimensional shape without sliding parts.
The hinge is a thin sheet of metal that maintains the correct angle and distance between adjacent solar cell panels when the array of panels is deployed. When the array is stowed, the metal is bent, that is flexed, within elastic limits. This stowage flexing stores energy that is later used to unfold the array after launch when the array is released. The hinge is a flexure type device that passively stores the energy required for deployment. After release, the hinges guide the panels during deployment and then maintains the desired deployment configuration once deployed. Thin sheets nitinol can bend around an extremely small radius without permanent deformation. When nitinol is raised in temperature to above the shape memory alloy transition training temperature, the nitinol will return to the trained configuration. When the trained sheet is released, the sheet springs back to the original shape. The on-orbit satellite releases the compressed stack of thin film panels that then unfold driven by the energy stored in the hinges located on the edges of each panel. To aid in rigidly holding the panels in place after deployment, the hinge is adapted to include an integral locking latch to hold the panel in the deployment configuration.
The shape memory metal alloy is formed as a thin film hinge structure that is simple in shape and easy to manufacture. The thin sheets of the nitinol alloy can be forged to provide the required precise final angle required to place each of the flat panels of the powersphere or powerbox into the deployment position. The superelastic shape memory alloy hinge is extended to include the function of a latch that locks the deployed structure in place for improved strength, and further functions as an electrical bus that conducts current from the solar cell panels to the payload of the satellite. Incorporating the stowage, deploying, latching and conductive functions in a single hinge element, the complexity and cost of the array is reduced, and the assembly process is simplified with improved reliability. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.